Linux/ts

ts

ts adds a timestamp to the beginning of each line of input

The optional format parameter controls how the timestamp is formatted, as used by strftime(3)
The default format is "%b %d %H:%M:%S"

ts 

-r # relative time ago (eg. 15m5s ago)
-i # incremental time
-s # time since program start
-m # monotonic clock

Timestamp Output

tail -f /some/device | ts